KRW Spherical roller bearings

Measures for prevention of damages by electrical current

26.03.2018

 

Traction motors of rail vehicles, in DC and AC motors in drive technology and in generators in wind turbines are often equipped with rolling bearings. If, from a constructive point of view, it is not possible to prevent the flow of current through the rolling bearings, it is mandatory to insulate the rolling bearing. If current passes through a rolling bearing,
massive damages can occur. Those often lead to total failure of the bearing and thus finally to a machine breakdown.

Fluting at the raceway caused by passage of current

Fluting at the raceway caused by passage of current

 

A first typical sign of current flow is the decomposition of the lubricant. As the damage progresses, micro craters unrecognizable to the unaided eye and a matting of the raceway
emerge. This is often mistaken for signs of an inadequate lubrication or associated with it. Caused by continuous rolling over the damaged area the failure develops to the
typical fluting.

 

KRW Bearing symbols - overview of the current isolated rolling elements

Variants of current-insulating coatings on rolling bearings (at the top), hybrid bearings with ceramic rolling elements (at the bottom)

 

We manufacture current-insulated rolling bearings that provide reliable protection against passing current. An oxide-ceramic insulating layer on the connection surfaces (lateral
surface and end face) of the bearing rings effectively prevents the passing of current through the bearing. Expensive conven-tional isolation methods become unnecessary.
We offer current insulation up to a breakdown voltage of 3000 V (DC) for all standard bearings and customized bearing types. Another option for current insulation is the use
of KRW hybrid bearings. Those bearings are equipped with ceramic rolling elements. Hybrid bearings provide a reliable insulation even at high AC voltages and temperatures.

 

KRW Bearing

Current isolation layer on the outer ring of a cylindrical roller bearing

 

The main dimensions of the current-insulated bearings are identical to standard bearings, what makes it easy to replace conventional with current isolated KRW bearings. If it is
not possible to insulate the rolling bearings, we also offer bearing insulating washers, which are used, for instance, for the protection of large thrust bearings. Current-insulated
bearings and insulating washers can be offered in diameters of more than 1 meter.

 

 

For further information please contact our sales team or our application engineering.